The world is getting warmer; we know this. But new claims suggesting that the temperature increase could be as high as 7 °C should be roundly ignored.
You may have already read about the study from which those numbers are drawn. Published in Nature, it suggests that the world is on course to experience warming in the next 1,000 years that’s beyond that of most conventional predictions. Keen to acknowledge the worst, some news outlets unquestioningly published the results, based solely upon Nature’s press release.
The research is impressive in some regards. It reconstructs the average surface temperature of Earth over the past two million years—far longer than the previous longest temperature record, which stretched back just 22,000 years (since about the end of the last Ice Age). That alone will be useful to climate scientists.
But the paper also uses its own data to estimate the sensitivity of Earth’s surface temperature to levels of carbon dioxide—and there it becomes unstuck. As Gizmodo points out, the research assumes that a historic correlation between global temperature and greenhouse-gas radiative forcing will hold in the future. The upshot is the suggestion that, based on today’s greenhouse-gas levels, a massive and unavoidable temperature rise of 3 to 7 °C will occur in the future.
But experts don’t think that’s valid. Speaking to Ars Technica, Richard Alley from Penn State said the predictions made by the researchers represented “an upper limit, because we know that some of the temperature change was not caused by greenhouse gases.” Speaking to Gizmodo, Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, was more blunt, saying: “This is simply wrong.”
The take-home message: the world is getting warmer—but not that much warmer. Chill out, people.